<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<link rel="stylesheet" href="./bootstrap-3.4.1-dist/css/bootstrap.css">
<style>
.row div{
    height: 50px;
    background-color: #ccc;
    border: 1px solid #999;
}
</style>
</head>
<body>
    
<!-- 
    栅格系统
    栅格系统主要用于响应式布局
    栅格系统一行自动分为最多12列
    预定义类：.col-xs-？	.col-sm-？	.col-md-？	.col-lg-？
    “行（row）”必须包含在 .container （固定宽度）或 .container-fluid （100% 宽度）中
    列表column必须在行row中使用
 -->

<div class="container-fluid">
    <div class="row">
        <div class="col-md-1">1</div>
        <div class="col-md-1">1</div>
        <div class="col-md-1">1</div>
        <div class="col-md-1">1</div>
        <div class="col-md-1">1</div>
        <div class="col-md-1">1</div>
        <div class="col-md-1">1</div>
        <div class="col-md-1">1</div>
        <div class="col-md-1">1</div>
        <div class="col-md-1">1</div>
        <div class="col-md-1">1</div>
        <div class="col-md-1">1</div>
    </div>
    <div class="row">
        <div class="col-md-4">4</div>
        <div class="col-md-4">4</div>
        <div class="col-md-4">4</div>
    </div>
    <div class="row">
        <div class="col-md-3 col-sm-6 col-xs-9">3</div>
        <div class="col-md-9 col-sm-6 col-xs-3">9</div>
    </div>
    <div class="row">
        <div class="col-md-4 col-md-offset-2">4</div>
        <div class="col-md-4 col-md-offset-2">4</div>
    </div>
    <div class="row">
        <div class="col-md-2">2</div>
        <div class="col-md-10">
            <div class="row">
                <div class="col-md-4">4</div>
                <div class="col-md-4">4</div>
                <div class="col-md-4">4</div>
            </div>
        </div>
    </div>
</div>

</body>
</html>